Practical Workbook Experiment #6 BJP TRANSISTORS

It's clear from all measurements above how to identify the transistor's electrodes.Vbe is always higher than Vbc. Once you pay attention what is the polarity of multimeter lead you attach to the base and collector or emitter you can easily find what type is the transistor. For NPN type if positive lead is attached to the base and negative to collector or emitter you have Vbe and Vce reading. For PNP transistor picture will be opposite.Negative lead is attached to the base and positive to collector or emitter. Thus, you can check if the transistor is working and also identify its type and mark the electrodes.

 Vbe shows that transistor base to emitter junction voltage drop slightly exceeds so-called 'knee voltage'.
Vce is that small because the transistor is fully opened.

In the A-region transistor is saturated. That means it's fully opened and Ic reaches its maximum while Vce is in minimum.
In the B-region, which is called cut off, transistor is closed.
To calculate power dissipation we can draw  lines to the load line on the graph. Then, we can find the Pd by multiplying Vce and Ic.
Beta that refer as Hfe as well, can be find from this graph also.
Hfe=Ic/Ib. The same technique of drawing lines to the vertical and horizontal axes is used to determine the Ic and Ib.

In Experiment No 8
we changed the Rb and checked what were changes for Vbe, Vce, Ib, Ic.

Rb is the limiting resistor in this case. By increasing Rb, we limit Ib from 90uA to 10uA. The lower Ib the closer transistor to the cut off region. That's why Vce rises during this experiment. We know that Ic is beta times Ib. So that, it goes down. To simplify, we experimented how transistor can be controlled by Ib.

The graph that is drawn above on the basis of the measurements from this experiment allow us to see how all these transistor's characteristics are interrelated. Another advantage of this graph is that it makes easier to understand how transistor change its working mode.The load line also allows to model amplifier and to see input and output signals relation.